The present invention relates to a wavelength-tunable, distributed Bragg reflector laser.
It more particularly applies to the field of optical telecommunications and makes it possible to obtain a very widely tunable monofrequency laser more especially usable for information transmission by optical fibre.
Various wavelength-tunable, semiconductor monofrequency lasers are known.
The distributed Bragg reflector laser or DBR laser can be discontinuously tuned (in jumps) with a small wavelength tuning range of approximately 10 nm and reference can be made in this connection to the following document:
(1) Y. Kotaki et al., "Wavelength tunable DFB and DBR lasers for coherent optical fibre communications", IEEE Proceedings-J; Vol. 138, No. 2, April 1991.
This known DBR laser has an active section (amplifying part) optically coupled to a passive guiding section, where is etched a Bragg grating permitting a monofrequency light emission. The wavelength tuning of such a laser is obtained by current injection into the section containing said grating.
The variation of the number of charge carriers in said section contributes to modifying the effective optical index of the section and therefore the emission wavelength of the laser.
Other lasers are known comprising Bragg gratings or more complex light guides and in this connection reference should be made to the following documents:
(2) Y. Yoshikuni et al., "Broadly tunable Distributed Bragg Reflector lasers with a multiple-phase-shift super-structure grating", paper TuC2, p.8 Proceedings OFC/IOOC'93, San Jose, U.S.A., 21-26 February 1993. IEEE Photonics Techn. Lett., Vol. 4, No. 4, April 1992.
(3) R. C. ALFERNESS et al., "Broadly tunable InGaAsP/InP laser made based on vertical coupler filter with 57 nm tuning range" Appl. Phys. Letters, Vol. 60, No. 26, 29 Jun. 1992.
These other known lasers make it possible to obtain a discontinuous tuning over a wide range of approximately 60 to 100 nm.
For all the known lasers referred to hereinbefore, the wavelength tuning capacity or wavelength tunability is based on the variation of the optical index by the injection of charge carriers into a light guiding section, which has a more or less complex Bragg grating.
In addition, the main disadvantages of most of the other lasers referred to hereinbefore in conjunction with documents (2) and (3) are the complexity of the Bragg grating or the light guide to be produced; the number of different electric currents having to be controlled in order to obtain said tunability; the limited number of accessible wavelength channels; the difficulty of controlling the spacing between said different wavelength channels; and the extreme complications encountered in continuously tuning said lasers.